This invention relates to vascular repair devices, and in particular intravascular stents, which are adapted to be implanted into a patient's body lumen, such as a blood vessel or coronary artery, to maintain the patency thereof. Stents are particularly useful in the treatment of atherosclerotic stenosis in arteries and blood vessels.
Stents are generally tubular-shaped devices which function to hold open a segment of a blood vessel or other body lumen such as a coronary artery. They also are suitable for use to support and hold back a dissected arterial lining that can occlude the fluid passageway. At present, there are numerous commercial stents being marketed throughout the world.
Balloon dilatation catheters are sometimes used to pre-dilate a diseased vessel prior to installation of a stent. Some balloon dilatation catheters include cutters, or atherotomes, which are placed longitudinally along the length of the balloon. The cutters create incisions in the vessel to provide greater control over the area of the vessel which stretches most during a balloon dilatation procedure. The incisions relieve pressure in the wall of the vessel, thereby enhancing dilation of the vessel by the balloon and allowing the vessel to be dilated more readily at a lower pressure. However, lesions are typically non-concentric, but the force from a balloon during a dilatation procedure is uniform. A nonuniform force distribution may not be desirable because the healthy portion of a vessel is typically the thinnest and weakest and consequently stretches more than the diseased portion. It is more desirable to deform the diseased portion of the vessel, such as a calcified lesion.
Further, some coronary arteries may develop vulnerable plaque which may require treatment through stenting. A vulnerable plaque is typically composed of a thin fibrous cap over a large lipid pool. It is sometimes desirable to rupture the fibrous cap during a stenting procedure and drain the lipid pool. Such a controlled rupture allows a physician to immediately respond to any complications such as a thrombus formation. What has been needed and heretofore unavailable is a stent that opens more easily in selected portions of the stent circumference compared to the remainder of the stent to increase stress on the diseased portions of the artery and reduce stress on healthy tissue. What also has been needed is a stent which induces stress to the fibrous cap which retains the vulnerable plaque during opening of the stent to cause rupture to the fibrous cap during the stenting procedure. The present invention satisfies these needs. The stent of the present invention includes portions of varying strength about its circumference. The stent also includes stress concentrators on the exterior portion of the stent. Each of these elements contribute to inducing more stress to the fibrous cap which retains vulnerable plaque and rupturing of the fibrous cap to effect a controlled release of vulnerable plaque contents during stent opening.